1. Field of the Invention
The present invention relates to a method for producing a semiconductor device and a structure for a semiconductor device, and it particularly relates to the method in which an electrode wiring with an improved planar process for the semiconductor device is achieved so that migration endurance is superior and there is caused no corrosion. The present invention further relates to an electrode wire structure in which wire reliability is improved, a wire resistance and contact resistance is reduced, a heat radiation effect for wiring is improved, a stress for the semiconductor device is relaxed, and a wiring adhesion is improved.
2. Description of the Prior Art
In the conventional practice, aluminum (Al) alloy in which Al is a major component is used as an electrode wire material for an LSI (Large-Scale Integration) circuit so as to form a wiring metal by etching a continuous film. However, a wire width and a thickness of wire film are minified due to an ever fine structure of the LSI circuit, so that there is caused a problem where a wire reliability therefor is inferior.
As causes for a low interconnection reliability, there can be considered an electromigration phenomenon and a stressmigration phenomenon. Hereinafter, terms wiring (wire) and interconnection are used interchangeably. Taking an example of Al here, the electromigration is an phenomenon where an electron flowing the interconnection collides with an Al atom so that the Al atom is transferred. The stress migration is a phenomenon in which the transfer of Al atom is caused by a mechanical stress of other material used for LSI. These phenomena have been known accordingly by a recent study.
In order to solve a problem of the low interconnection reliability, that a crystal orientation of Al interconnection is controlled has been examined. An Al crystal has a face centered cubic structure and an surface energy thereof is minimum in a (111) face. Therefore, when an Al film is formed by a sputtering method or the like, a &lt;111&gt; direction is normal to the substrate such that the surface energy is minimum.
When the preferred &lt;111&gt; direction oriented normal to the substrate is further improved, the probability that a (111) face having a minimum surface energy faces with the (111) face at a wire cross section is decreased, so that a slit-like disconnection due to the stressmigration is decreased and the interconnection reliability can be improved.
However, though the &lt;111&gt; preferred orientation is indicated when the Al is formed by the convention sputtering method, a fine crystal grain at an early stage of film formation reaches immediately with a neighboring fine crystal grain. The Al which became a continuous film accordingly is affected each other between neighboring crystal grains, so that the preferred &lt;111&gt; direction oriented normal to the substrate is deteriorated. In other words, there is problem in the conventional practice where the preferred &lt;111&gt; direction is deteriorated due to interaction between crystal grains under the conventional formation method.
Moreover, the further preferred orientation of &lt;111&gt; in Al can not completely control an in-plane orientation of crystal grain in a surface, so that the grown Al film becomes polycrystalline oriented in the preferred &lt;111&gt; direction oriented normal to the substrate. When a semiconductor device is formed by such Al film in a manner described above, there exist a great deal of crystal grain boundaries in a wiring region. The crystal grain boundaries in the wiring region is considered as a set of lattice defect, so that a structure thereof is unstable and a diffusion coefficient for the Al atom in the grain boundary is rather big.
Therefore, the electromigration occurs in a manner that a transfer of Al atom up to the grain boundary occurs in a same rate and the rate the transfer of Al atom is increased at the grain boundary. In other words, there occurs a depletion of atom in an upstream side where the Al atom flows apart from the crystal boundary, and there occurs an accumulation of atom in a downstream side. The depletion of atom may cause a disconnection of interconnection, and the accumulation of atom may cause hillocks.
Moreover, when a mechanical stress is applied to the Al interconnection, the atom thereof tends to move in a direction where the stress is relieved. Then, the transfer of Al atom is likely to occur for the grain boundary in the interconnection, so that the atom of the grain boundary is depleted and the interconnection is disconnected. Among such grain boundaries, when the neighboring crystal grains are crystal grains with a micro inclination rotation, diffusion of the Al atoms in the grain boundaries are slow so as to have a certain tolerance against the respective migrations mentioned before.
However, an improvement of the preferred &lt;111&gt; orientation is not considered and the in-plane orientation control is not performed in the (111) face of the crystal grains in case of forming the Al film in the conventional production process of the semiconductor devices. Thus, though the formed Al film indicates the preferred &lt;111&gt; orientation normal to the substrate, the orientation is not sufficient and each crystal grain rotates randomly in the (111) face. Therefore, there is a problem where the interconnection is likely to be disconnected due to the fact that the conventional Al interconnection lacks endurance against the electromigration as well as the stressmigration.
A resistance value of the interconnection relates to a R--C (resistance-capacitance) delay and is an important factor which determines an operational speed of the semiconductor device, so that a low resistance is required. As miniaturization of the device becomes significant, the low resistance is also required in terms of a self-heating problem in the interconnection. However, there is a limit in a material in terms of the low resistance in the conventional Al alloy interconnection, so that a change to a new wiring material is necessary.
As for material such as Cu and Ag that have a lower resistance than Al-containing material, it is hard to form a compound having a high vapor pressure. Thus there is a problem where a process is rather difficult to be performed by a dry etching such as the conventional reactive ion etching (RIE). Moreover, there is a problem where corrosion is likely to occur due to an effect by a residual etching gas even for Al in which the process is relatively easy.
Moreover, the conventional interconnection formed using the RIE method is of a projection type. Therefore, there is needed a planar process for an interlayer insulator which is later formed, thus causing to increase the number of processes and creating a problem where a sufficient planar degree cannot be obtained.
On the other hand, in the conventional polycrystalline Al multilayer interconnection structure, it is likely that a mechanical stress remains behind at the time of forming the interlayer insulator. As a consequence, such structure is weak against the stressmigration and the interconnection is likely to be disconnected.
Moreover, in the conventional multilayer wiring structure, an upper wiring metal is formed after a contact hole is opened, so as to connect an upper wire and a lower wire. When Al is formed by a usual sputtering method, there are problems where a characteristic of step coverage is inferior, a bench-cut occurs, and a contact resistance is increased.
In order to alleviate such problems, a different metal such as W is filled as a plug into the contact hole in the conventional practice, so as to prevent a bench-cut defect. However, when used as the plug is the different metal from the upper and/or lower interconnections, an interconnection metal atom transferred due to the electromigration and stressmigration phenomena is hindered from the transfer thereof on account of the plug. When W is used, for instance, as the plug, W presents an excellent endurance against the electromigration and stressmigration compared to Al.
Therefore, in a cathode side of the W plug, the Al atoms transferred through the interconnection are accumulated and the hillock is formed, while, in an anode side of the plug, the Al atoms are depleted and the void is formed.
Moreover, even when the plug is formed by the same metals, there exist a native oxide film and a grain boundary between the plug and the upper layer interconnection, thus causing problems where migration endurance is deteriorated and the contact resistance is increased.
Moreover, as a result of miniaturization of interconnection, there flows a high-density current through the interconnection, thus causing problems where a wiring resistance is increased and the operational speed of the device is slowed down due to a self-heating of the interconnection.
Moreover, the conventional wiring patterns are of the structure where the mechanical stress is likely to occur to a substrate, thus causing defect due to the stress.
Accordingly, an electrode interconnection which is formed by the conventional method is inferior in the electromigration and stressmigration endurance, so that reliability for interconnection is low.
Moreover, the processing is difficult to be performed for the low-resistance wiring metal. Besides, there is a problem where the corrosion occurs due to the remaining etching gas even for the easy-to-process metal such as Al.
Moreover, there are problems where the number of processing is increased in order to achieve planarization and a degree of planarization is not desirable in the conventional interconnection.
Moreover, there are problems where, in the conventional multilayer interconnection, crystallinity deteriorates due to the mechanical stress generated in the course of forming the interlayer insulator on the interconnection, so that the reliability for interconnection deteriorates and the contact resistance between the upper layer and lower layer interconnections, between the upper layer interconnection and the plug, or between the plug and the lower layer interconnection. Moreover, there is a problem of the self-heating of the interconnection.
Moreover, there is a problem of poor migration endurance against between the metal plug differing from the interconnection metal and upper-and-lower layer interconnections.